This is why it might happen. Not saying it will.
1) One poll has undecided voters at 14 percent on the last weekend, which means most of them probably really aren’t undecided, that they are either going to stay home or vote preponderantly for McCain and pull McCain across the finish line.
2) Most pollsters are claiming the electorate this year is six to nine points more Democratic than it is Republican. That would be an unprecedented shift from four years ago, when the electorate was evenly divided, 37-37, Republican and Democratic, and a huge shift from two years ago, when it was 37-33 Democratic. A shift of this size didn’t even happen after Watergate.
3) Obama frequently outpolled his final result in primaries, which might have many causes but might also indicate that he has difficulty closing the sale.
4) The argument in the past two weeks has shifted, such that many undecided voters who are now paying attention are hearing about Obama’s redistributionist tendencies at exactly the right moment for McCain.
5) The tightening in several daily tracking polls indicates a modest surge on McCain’s part that could continue through the weekend until election day. If he is behind by three or four points right now, a slow and steady move upward could push him past the finish line in first place.
6) In terms of the electoral map, the energy and focus McCain is directing at Pennsylvania could pay huge dividends if he pulls it off. If he prevails there, it might follow that the message will work in Ohio too. And if he wins Pennsylvania and Ohio, he will probably win even if he loses Virginia and Colorado.
7) Early voting numbers are not oceanic by any means, which may indicate the degree of enthusiasm for Obama among new voters is not something new but something entirely of a par with past candidates, like John Kerry. And they show more strength on the Republican side than most people expected.
8) What happened with the Joe the Plumber story is that Obama has now been effectively outed as a liberal, not a moderate; and because liberalism is still less popular than conservatism, that’s not the best place for Obama to be.
9) The fire lit under Obama’s young supporters in the winter was largely due to Iraq and his opposition to the war. The stunning decline in violence and the departure of Iraq from the front page has put out the fire, to the extent that, like the young woman who made a sexy video calling herself Obama Girl and then didn’t vote in the New York primary because she went to get a manicure, they might not want to stand on line on Tuesday.
10) Hispanic voters, who are always underpolled, know and appreciate McCain from his stance on immigration and will vote for him in larger numbers than anyone anticipates.
There you have it. It’s admittedly not the strongest case, and the idea that McCain will win on Tuesday is hard to square with the fact there isn’t a single poll that has him in the lead five days out. But unexpected things do happen in politics every election.